1. Field of the Invention
This invention relates to force measuring systems. In particular, this invention pertains to force measuring systems which provide for an electrical output responsive to an applied force loading. More in particular, this invention relates to a shear beam load cell utilizing shear type strain gauges to measure the force loading. Still further, this invention pertains to a shear beam load cell system which provides for integral flexure isolation mechanisms. Further, this invention relates to a shear beam load cell system which utilizes particular geometries and contours to aid in stability, as well as to maximize the linearity of the electrical output to provide a more accurate force measurement reading.
2. Prior Art
Load cell systems for measuring force applied to the cell are well-known in the art. Some prior art force load cells were constructed devoid of swivels or flexure isolation means. In general, all load cells should be constructed to be as insensitive to off-center force loading as possible, since force errors occur in various weighing processes. In some prior art load cells, the sensitivity to off-center loading was unacceptable, thus requiring the platform to be stabilized in order that such did not shift its position responsive to the force load location.
Such stabilization systems used various contoured bar members, as well as flexured members. These prior art stabilizing systems increased the costs dramatically of the overall weighing systems and due to space requirements, were in many cases found to be non-installable. Additionally, when the above-referenced stabilization systems were used in conjunction with the prior art load cell systems, the apparent sensitivity of each load cell in the same overall weighing system was found to be a dependent parameter on the other load cells. Thus, where one load cell was de-sensitized, other load cells may have been sensitized to off-center loading.
Additionally, high capacity scale calibration is generally cumbersome as well as expensive. In general, multiple load cells are electrically interconnected by paralleling the electrical inputs/outputs to a strain gauge bridge. In such prior art systems, it was necessary to install potentiometers at the input to the load cells in order to match the output sensitivity of each load cell. Since the load cells are in electrically parallel connection, the adjustment of any one load cell potentiometer affects the sensitivity of other load cells in the overall system. The electrical interaction has made it a rather slow process to equalize electrical outputs from each load cell in an overall scale system. By minimizing the sensitivity to off-center loading for the present load cell system, such eliminates the need for prior art stabilizing systems and essentially eliminates the need for potentiometer output equalization.
In some prior art load cell systems, an attempt was made to minimize the sensitivity to off-center loading. Cantilever shear beam systems are known in the art. However, cantilever shear beam load cells have an increased size for a given capacity when taken with respect to the subject shear beam load cell system. Additionally, prior art cantilever beam load cells must be large enough to support mounting bolts or other type fastening mechanisms required to hold the leverage from a cantilever type mounting. Since prior art cantilever type beams require large mounting surfaces, such prior art load cells include large wasted areas which cannot be utilized for the force measuring. In some prior art shear type load cells, such as that shown in U.S. Pat. No. 3,985,025, the webs and overall beams are generally rectangular in contour. Such rectangular or square cross-sectional areas are difficult to mate with other hardware used in the overall system. Thus, such prior art systems are generally machined parallel and mating hardware must rely on extremely close tolerances. Additionally, in such prior art shear measuring load cell systems, the beams are fixed at both ends and in many cases have been found to buckle and form an unwanted undulating configuration. These types of prior art load cell systems thus require increased space installation volumes, increased machining and expended labor costs in order to provide an off-center load desensitization aspect to the overall system.